Anatomically shaped vasoocclusive device and method of making the same

ABSTRACT

This invention is an occlusive device for inserting into body cavities or vesicles. More particularly, it is a vasoocclusive device which, as used, is in the approximate shape of an anatomical cavity. It may be ultimately deployed as a substantially spherical shape in the operable configuration. The device is a self-forming shape made from a pre-formed occlusive strand of flexible material. The occlusive strand may be helically coiled or braided and may be adapted with various polymeric fibers. The device is typically introduced through a catheter in the substantially linear inoperable configuration. The invention provides a plurality of such substantially spherical strand portions which nest concentrically with each other in the operable configuration. The invention also includes methods of producing and using the substantially spherical occlusive devices.

This is a continuation of application Ser. No. 08/799,439 filed Feb. 13,1997, now U. S. Pat. No. 5,766,219, which is a continuation of Ser. No.08/425,106 filed Apr. 20, 1995 (now U.S. Pat. No. 5,645,558).

FIELD OF THE INVENTION

This invention relates to the field of vasoocclusive devices. Moreparticularly, it relates to a vasoocclusive device which, as used, is inthe approximate shape of an anatomical cavity. The devices may beultimately deployed through a catheter.

BACKGROUND OF THE INVENTION

Vasoocclusion devices are surgical implants that are placed within thevasculature of the human body, typically via a catheter, either to blockthe flow of blood through a vessel making up that portion of thevasculature through the formation of an embolus or to form such anembolus within an aneurysm stemming from the vessel. One widely usedvasoocclusive device is a helical wire coil having windings which may bedimensioned to engage the walls of the vessels. Other less stiffhelically coiled devices have been described, as well as those involvingwoven braids.

For instance, U.S. Pat. No. 4,994,069, to Ritchart et al., describes avasoocclusive coil that assumes a linear helical configuration whenstretched, and assumes a folded, convoluted configuration when relaxed.The stretched configuration is used in placing the coil at the desiredsite, e.g. by its passage through a catheter. Once the device is soplaced, the coil assumes a relaxed configuration, which is better suitedto occlude the vessel. Ritchart et al. describes a variety of shapes.The secondary shapes of the disclosed coils include "flower" shapes anddouble vortices. A random shape is described, as well. These priorvasoocclusive devices do not maintain a three-dimensional conformationfor a satisfactory period of time; the coils collapsing in uponthemselves to form mere rings. A useful substantially sphericalvasoocclusive device has heretofore not been made available.

Vasoocclusive coils having attached fibrous elements in a variety ofsecondary shapes are shown in U.S. Pat. No. 5,304,194, to Chee et al.Chee et al. describes a helically wound device having a secondary shapein which the fibrous elements extend in a sinusoidal fashion down thelength of the coil. These coils, as with Ritchart et al., are producedin such a way that they will pass through the lumen of a catheter in agenerally straight configuration, and when released from the catheter,form a relaxed and folded shape in the lumen or cavity chosen within thehuman body. The fibrous elements shown in Chee et al. enhance theability of the coil to fill the space within the vasculature and tofacilitate formation of embolus and subsequent allied tissue.

There are a variety of ways of discharging shaped coils and linear coilsinto the human vasculature. In addition to those patents whichapparently describe only the physical pushing of a coil out into thevasculature (e.g., Ritchart et al.), there are a number of other ways torelease the coil at a specifically chosen time and site. U.S. Pat. No.5,354,295 and its parent, U.S. Pat. No. 5,122,136, both to Guglielmi etal., describe an electrolytically detachable embolic device.

A variety of mechanically detachable devices are also known. Forinstance, U.S. Pat. No. 5,234,437, to Sepetka, shows a method ofunscrewing a helically wound coil from a pusher having interlockingsurfaces. U.S. Pat. No. 5,250,071, to Palermo, shows an embolic coilassembly using interlocking clasps mounted both on the pusher and on theembolic coil. U.S. Pat. No. 5,261,916, to Engelson, shows a detachablepusher-vasoocclusive coil assembly having an interlocking ball andkeyway-type coupling. U.S. Pat. No. 5,304,195, to Twyford et al., showsa pusher-vasoocclusive coil assembly having an extending wire carrying aball on its proximal end and a pusher having a similar end. The two endsare interlocked and disengage when expelled from the distal tip of thecatheter. U.S. Pat. No. 5,312,415, to Palermo, also shows a method fordischarging numerous coils from a single pusher by use of a guidewirewhich has a section capable of interconnecting with the interior of thehelically wound coil. U.S. Pat. No. 5,350,397, to Palermo et al., showsa pusher having a throat at its distal end and a pusher through itsaxis. The pusher sheath will hold onto the end of an embolic coil andwill then be released upon pushing the axially placed pusher wireagainst the member found on the proximal end of the vasoocclusive coil.

Vasoocclusive coils having little or no inherent secondary shape havealso been described. For instance, in U.S. patent application Ser. No.07/978,320, filed Nov. 18, 1992, entitled "Ultrasoft Embolization Coilswith Fluid-Like Properties" by Berenstein et al., is found a coil havinglittle or no shape after introduction into the vascular space.

Common to all of these devices described above is the characteristic oflacking a spheroid shape when relaxed. Additionally, the concept of aplurality of concentrically nested spherical vasoocclusive devices islacking in the prior art.

SUMMARY OF THE INVENTION

This invention is a vasoocclusive device comprising one or more strands,or vasoocclusive members, which are wound to form a generally sphericalor ovoid shape when relaxed. The strand is made of a flexible materialmovable between an inoperable substantially linear configuration forinsertion into and through a means for delivering the device to acavity, and an operable, substantially spherical configuration foroccluding at least a portion of said cavity.

The vasoocclusive member itself may be a helically wound coil or aco-woven braid typically comprising a biocompatible metal. Fibrousmaterials may be woven into the member or tied or wrapped onto it.Desirably, in the operable configuration, the device is of a size andshape suitable for fitting snugly within a vascular cavity or vesicle(e.g., an aneurysm, or perhaps, a fistula). The device may be adaptedwith multiple portions of different substantially spherical sizes, whichwhen relaxed and in the operable configuration nest concentrically, ornon-concentrically, with each other within the vascular cavity.

The device may be made in a variety of ways. Typically, the strand isfirst helically wound or braided in a generally linear fashion. Aftercompletion of that step, the strand is then wound around anappropriately shaped mandrel or form and heat-treated in such a fashionthat it will retain its shape after removal from the heating form.Auxiliary fibrous materials are then added by weaving, tying, or othersuitable permanent attachment methods.

The device is used simply by temporarily straightening the device intothe inoperable configuration and introducing it into a suitablecatheter, the catheter already having been situated so that its distalopening is within the mouth of the vascular crevice or opening to befilled. The device is then pushed through the catheter and, upon itsemanation at the distal end of the catheter into the vascular cavity,assumes its relaxed operable configuration.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a side view of a spherical device made according to theinvention.

FIG. 2 shows a side view of a device having an oval cross-section madeaccording to the invention.

FIG. 3 shows a side view of a device made according to the inventionusing a thrombogenic fiber.

FIG. 4 shows a magnified section of a helical coil as could be used inthe inventive device having filamentary material attached through theloop of the device.

FIG. 5 shows a magnified section of a helical coil covered by an outerfibrous braided covering.

FIG. 6A shows a central cross-section of an alternative embodimenthaving a vasoocclusive sphere covered with fibers positioned within afirst vasoocclusive sphere as it would appear when deployed within aportion of a vesicle.

FIG. 6B shows a side view of the alternative embodiment shown in FIG. 6in the wound configuration, but not deployed in a vesicle.

FIG. 7 shows a mandrel suitable for winding making a device according tothe invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows one highly desirable embodiment of this invention, asubstantially spherical occlusive device (100) in the operableconfiguration. The occlusive device (100) comprises at least one strand(102) of flexible material movable between an inoperable substantiallylinear configuration for insertion into and through a means fordelivering the device to a desired portion of a vesicle, and anoperable, substantially spherical configuration for occluding at least aportion of said vesicle. Preferably, the vesicle is an artery and thedesired portion is an aneurysm, however, the invention contemplates thatany bodily vesicle or cavity may be occluded by the device. The strand(102) shown is wound in a tertiary substantially spherical structure soas to have multiple loops spaced generally equally to form a cavity, orcage-like structure. The rear side strand (102) loops are shown asdotted lines for clarity, however, these would be visible through theopen areas of the cage. It is clearly not necessary that the tertiaryshape be precisely a sphere, but it is desirable from a mechanical pointof view that such a spacing be approached. The invention contemplatesthat the occlusive device (100) is wound into and is self-forming into asubstantially spherical or distorted spherical form.

In one embodiment, it is intended that the device (100) in the operableconfiguration be in a roughly spherical cavity or cage-like structurewhere at least 90-95% of the strand (102) is in the outer 10-15% of thediameter of the device (100). The precise number of loops of the strandwill vary and depends upon the type of vesicle or cavity to be filled,and upon the length of catheter tubing necessary for deployment in theextended, linear position.

FIG. 2 shows a variation of the invention in side view in which theshape of the anatomically conforming vasoocclusive device (104) is ovalor egg-shaped, yet still substantially spherical in the operableconfiguration. Other than the final shape of the FIG. 2 device (104), itis similar to that shown in FIG. 1. It is of little importance whichaxis of the ovoid structure is the major axis and which is the minoraxis. In general, it is desirable that the device (104) be constructedin such a way that the resulting relaxed device (104) have a shapesimilar to the cavity into which it is placed. Somewhat less sphericalconfigurations of the device are permissible and, in many instances,even desired, depending upon the anatomical shape of the vesicle orcavity to be occluded. The substantially spherical shape prevents thevasoocclusive device from collapsing upon itself. By the term"substantially spherical" is meant a shape which includes spherical aswell as other distorted shapes, such as ovate, ovoid, or ellipsoid, butin any event having two orthogonal cross sections which are closedshapes having no substantially straight sides.

The material used in the occlusive device (100) may be any of a widevariety of materials. Preferably, the strand (102) is a wire constructedof a radiopaque material such as a metal or a polymer. Suitable metalsand alloys for the wiring include Platinum Group metals, especiallyplatinum rhodium palladium, as well as tungsten, gold, silver, tantalum,and alloys of these metals. Highly preferred is a platinum/tungstenalloy.

The wire may also be of any of a wide variety of stainless steels ifsome sacrifice of radiopacity may be tolerated. Very desirable materialsof construction, from a mechanical point of view, are materials whichmaintain their shape despite being subjected to high stress. Certain"super-elastic alloys" include nickel/titanium alloys (48-58 atomic %nickel, and optionally containing modest amounts of iron); copper/zincalloys (38-42 weight % zinc); copper/zinc alloys containing 1-10 weight% of beryllium, silicon, tin, aluminum, or gallium; or nickel/aluminumalloys (36-38 atomic % aluminum). Particularly preferred are the alloysdescribed in U.S. Pat. Nos. 3,174,851; 3,351,463; and 3,753,700.Especially preferred is the titanium/nickel alloy known as nitinol.These are very sturdy alloys which will tolerate significant flexingwithout deformation even when used as a very small diameter wire.Additionally, the strand may be constructed of a polymer, such aspolyvinyl alcohol foam, for example.

Generally speaking, when the device (100) is formed of a metal such asplatinum or a super-elastic alloy such as nitinol, the diameter of thewire used in the production of the coil will be in the range of 0.0005and 0.006 inches. The wire of such diameter is typically then wound intoa coil having a primary diameter of between 0.005 and 0.018 inches. Thepreferable diameter is 0.010 to 0.018 inches. The wire should be ofsufficient diameter to provide a hoop strength to the resulting devicesufficient to hold the device (100) in place within the chosen bodycavity without distending the wall of the cavity and without moving fromthe cavity as a result of the repetitive fluid pulsing found in thevascular system. Obviously, should a super-elastic alloy such nitinol beused, the diameter of the coil wire can be significantly smaller thanthat used when the relatively ductile platinum or platinum/tungstenalloy is used as the material of construction. Finally, as regards FIG.1, the overall diameter of the device (100) in the operableconfiguration is generally between 3 and 40 millimeters. Most aneurysmswithin the cranial vasculature can be treated by one or more deviceshaving those diameters.

As can be seen in FIG. 3, the occlusive strand (107) may be adapted withfibers (108) such as synthetic radiolucent fibers or polymers (ormetallic threads coated with radiolucent or radiopaque fibers) such asdacron (polyester), polyglycolic acid, polylactic acid, fluoropolymers(polytetrafluoro-ethylene), nylon (polyamide), or even silk. Naturalfibers such as silk, cotton or wool may also be employed. Should a fiberbe used as the major component of the strand (102), it is desirablyfilled with some amount of a known radiopaque material such as powderedtantalum powdered tungsten bismuth oxide, barium sulfate, and the like.

The fibrous elements incorporated into the braid may be a bundle ofindividual fibers, e.g., between 5 and 100 fibers per fibrous bundle,preferably 20-30 fibers per bundle, or may be monofilaments. As wasnoted above, it may be desirable in certain circumstances to add fibrousmaterials outlying the vasoocclusive core so to provide additional bulkand area for creation of thrombosis.

FIG. 4 shows a magnified side view of a portion of a helically coiledvasoocclusive strand (110) as may be used in the variations of theinvention. Shown attached to the coiled vasoocclusive strand (110) arefibrous polymeric materials (112, 114) attached to the member (110) bydistinct two methods. First is a series of looping fibers (112), whichare looped through or tied to the strand (110) and continue axially downthe coil. Another variation is the tuft (114) shown tied or otherwiseaffixed to the strand (110). Tufts (114) are tied at multiple sitesthrough the coiled strand (110) so to provide a vast area of thrombusforming sites.

The occlusive strand (110) in FIG. 4 is shown to have a secondarystructure of helically wound flexible material. The helixes providefurther support to the substantially spherical form when in the operableconfiguration. In another variation of the invention in which the devicecan comprise a plurality of small, braided strands (not shown). Thestrands can be braided elements made partially of regularly or randomlyincluded radiopaque wires. Again, the braid may optionally be partiallywoven of, or co-woven with, fibers. The wire or fibers used in theproduction of the braid will typically be fairly small, e.g., in therange of 0.0005 to 0.0015 inches. The resulting woven braid diameterwill normally be 0.008 to 0.018 inches. The braided structure istypically not as compliant as is that of a coiled secondary structure.Consequently, a more ductile material such as platinum may be preferablein such a device. The braid structure permits introduction of natural orsynthetic fibrous materials such as Dacron and the other filaments notedbelow which promote formation of a thrombus.

Additionally, the invention contemplates that a safety wire (not shown)may be inserted through the longitudinal axis of the helically coiledstrand to provide structural support. Alternatively, the safety wire maybe first formed to be flexibly disposed in a substantially sphericalform, and then inserted through the longitudinal axis of a helicallycoiled strand which has not been preformed in a substantially sphericalform.

FIG. 5 shows still another variation and method for increasing thethrombogenic capability and rate of the device. FIG. 7 shows an embolic,helically shaped strand (116) co-woven with and covered by a fibrousbraid (118). One method for producing the variation shown in FIG. 6 isdescribed in U.S. Pat. Nos. 5,226,911 and 5,304,194 to Chee. One mannerof producing the variation shown in FIG. 7 is described in U.S. patentapplication Ser. No. 07/965,973, filed Oct. 26, 1992, to Phelps andVann. One manner of making a co-woven braid using radiopaque fibers isshown in U.S. patent application Ser. No. 08/005,478, filed Jan. 15,1993, to Engelson and Samson. Each of these techniques may be used inmaking the vasoocclusive devices described herein however, other similartechniques will be known to the skilled artisan.

It is within the scope of this invention that procedures forincorporating first substantially spherical occlusive devices of thisinvention into an aneurysm or other vascular vesicle can be followed byintroduction of other occlusive devices into the center of the cavityformed by the first occlusive device to produce superior physicalstability.

FIG. 6A shows a cross-section of such an alternative embodiment of theinvention, wherein two vasoocclusive strand portions (142, 144) areprovided to nest concentrically with each other in the operableconfiguration. The larger vasoocclusive strand portion (142) can serveas a cavity in which to concentrically house the other smallervasoocclusive strand portion (144). When the device (140) is unwound inthe inoperable configuration, each vasoocclusive strand portion (142,144) is aligned longitudinally in tandem. Such a vasoocclusive device(140) with a plurality of concentric vasoocclusive portions can be madefrom the same metallic strand along different portions thereof, orseparate strands can be prepared and then fused together at their endsin longitudinal tandem. FIG. 6B shows this alternative embodiment in apartially unwound position to demonstrate that the spheres are arrangedin tandem along the same strand. The aligned vasoocclusive strandportions (142, 144) can each be wound on the same or slightly differentsized mandrel in order to form a multiple-layered sphere when positionedin the wound, operable configuration.

The invention contemplates that a plurality of concentrically nestingocclusive strand portions may be employed. Each spherical occlusivestrand portion may have a unique size, so that the device is capable ofconcentric nesting with the other occlusive members. The invention alsocontemplates that a plurality of substantially spherical strandportions, or other known vasoocclusive devices, can be inserted in anon-concentric manner inside a substantially spherical cavity created bythe first strand portion. To protect flowing blood from a thrombogenicsurface, the outermost coils may be bare, or unfibered. Providingnatural or synthetic fibers (146) to the innermost strand portion (144)increases the thrombogenicity therein and protects the vesicle fromflowing blood. In this way, blood clotting begins in the center of thevasoocclusive device and proceeds outward, stopping at the arteriallumen.

FIG. 7 depicts a mandrel (120) suitable for making a substantiallyspherical vasoocclusive device. As shown, the mandrel (120) canprimarily consist of a core (124). The core (124) is typically made of arefractory material, such as alumina or zirconia. The function of thecore (124) is simply to form a support for winding that will not pollutethe vasoocclusive device during the heat-treatment step to be describedbelow, and will provide a specific substantially spherical form for thevasoocclusive device during the heat-treatment step. Circumferentiallycontinuous grooves (122) on the surface of the core (124) may bepreferably provided to assist in regularly aligning the strand as it isbeing wound about the core (124). Additionally, a small strandreceptacle (126) may be provided to insert and hold the end or ends ofthe strand in place when performing the heating step. Other methods ofwinding a strand around a core will be apparent to one skilled in theart. The continuous grooves (122) are preferably provided to permit thestrand to be wound about the core (124) with minimal kinking orangulation of the coils.

If the entire then-wound vasoocclusive device is metallic, it may beplaced in an oven at an appropriate temperature to "set" or impart thesubstantially spherical form to the device. If the device is a platinumalloy or of nitinol, such a temperature is 1100 degrees Fahrenheit, for4 hours to provide a modest amount of preshaping to the resultingvasoocclusive device. Should the make-up of the vasoocclusive device notbe solely metal, in that it contains readily meltable plastic or thelike, the temperature at which the heat treatment takes place issignificantly lower and typically for a significantly shorter period oftime. The flexural modulus of most plastics being significantly lowerthan that of metals, the bulk of the polymer-based device will besignificantly larger than that of the metal-based device.

After cooling, the device is removed from the core (124). Anyfilamentary fibrous material may then attached to the strand asdescribed above. The vasoocclusive device is then placed in a cannula orcatheter for delivery in the inoperable substantially linearconfiguration into a selected body cavity or vesicle, where it thenassumes the operable substantially spherical configuration.

Practitioners in this medical device area will undoubtedly have otherways of producing the noted anatomically shaped occlusive andvasoocclusive devices. The vasoocclusive devices of this invention maybe used in a manner similar to those methods described in U.S. Pat. No.4,994,069. Briefly, the inventive devices are typically to supplied in aprepackaged form in a sterile cannula which is adapted to engage theproximal end of a catheter. Once the catheter is in place within avessel and the distal end of the catheter is placed into, e.g., a mouthof an aneurysm, the vasoocclusive device is inserted into the aneurysm,where it assumes its relaxed shape. Although the device may be used witha flexible pusher without connection to the vasoocclusive devicedescribed here, much more desirable is the use of a mechanicallydetachable coupling on the vasoocclusive device and the pusher. Any ofthe mechanically detachable couplings described above in the Backgroundof the Invention would be suitable in this instance.

Throughout this application various publications are referenced. Thedisclosures of these publications in their entireties are herebyincorporated by reference into this application in order to more fullydescribe the state of the art to which the invention pertains.

The examples herein are intended to illustrate, but not limit, thepresent invention. While they are typical of those that might be used,other procedures known to those skilled in the art may alternatively beemployed.

EXAMPLE

Transparent, elastic, vesicle models were constructed with two rows oflateral wall aneurysms for comparison: two each at diameters of 10, 8,6, and 4 millimeters. One row had narrow necks (less than 50% ofaneurysm diameter), the other had wide necks (greater than 50% ofaneurysm diameter). The models were perfused with both Newtonian andwith non-Newtonian fluids flowing at physiologic volumes and pulseprofiles. Isobaric dyes were injected and the flow dynamics observed.Various sizes and kinds of previously known coils, such as the GuglielmiDetachable Coil were, delivered to the aneurysms, in addition to varioussizes of the devices of the present invention, and the changes in flowdynamics were observed and compared.

The angular velocities within the aneurysm were observed to varyinversely with aneurysm diameter. That is to say that smaller aneurysmshad a faster angular flow velocities, however, both small-neck aneurysmsand wide-neck aneurysms were observed to have high angular flowvelocities. Aneurysms with wider necks were observed to have more rapidperipheral flow than those with smaller necks.

The spherical vasoocclusive devices of the present invention introducedinto the aneurysms markedly decreased the angular and peripheralvelocity by creating more internal friction and/or by better insulatingthe fluid in the aneurysm from that section of the parent artery. Suchan improved stasis of blood flow is critical to the success of theinvention to promote blood clot formation. As compared to otheravailable coils tested, the vasoocclusive devices of the presentinvention were very surprisingly successful and yielded unexpectedlyimproved results.

The vasoocclusive devices remained stable and in a substantiallyspherical form within the aneurysms, especially that made from0.004-inch platinum wire and inserted into the smaller aneurysms. Thiswas in contrast to the other available coil devices tested, which had atendency to collapse into ring forms when disturbed, as by theintroducing catheter tip. In larger aneurysms, especially those withwide necks, the greater hoop strength of the vasoocclusive devices ofthe present invention provided the desirable physical stability withinthe aneurysm.

What is claimed is:
 1. A method of making an occlusive device comprisinga strand of a flexible material movable between an inoperablesubstantially linear configuration for insertion into and through ameans for delivering the device to a desired portion of a vesicle, andan operable, substantially spherical configuration for occluding atleast a portion of said vesicle, the method comprising the stepsof:winding a strand of flexible material including a radiopaque materialonto a core having a substantially spherical form; heating the core andthe strand to impart a substantially spherical form to said strand; andremoving said strand from said core, thereby producing said occlusivedevice.
 2. The method of claim 1, wherein said step of heating comprisesheating the core and the strand to approximately 1100° F.
 3. The methodof claim 1, further comprising the step of connecting at least one fiberconnected to said strand.